The present invention relates to the field of printing presses and in particular to an apparatus for forming a printing plate to be secured to a press.
In printing presses, and in particular offset presses, printing is accomplished by transferring ink from an ink roller onto a plate cylinder, which holds a printing plate. The printing plate contains an image to be imparted on a substrate such as a sheet of paper or envelope. Printing plates are typically wrapped around the circumference of the plate cylinder so that it is covers the cylinder""s outer cylindrical. During the printing process, the printing plate rolls against a blanket cylinder, which in turn transfers the image to the substrate through an offset printing technique well known in the art. In other known printing processes, the plate cylinder may directly contact the substrate to be printed.
Printing plates are typically designed to be removably secured to the plate cylinder in order to facilitate relatively easy changing of the printing plate. Changing of printing plates is required when a different image is to be transferred to the substrate. Therefore, the use of removable printing plate permits a printing press to be readily configured to print different images. In addition, a printing plate is only good for a certain amount of printings before the image begins to deteriorate. Therefore, after a particular number of printings, a new printing plate can be substituted and additional printings made.
Printing plates are typically made of a metallic material, such as aluminum, having a photosensitive layer on which the image to be printed is fixed. The common method for attaching the printing plate to the plate cylinder is to insert the leading and trailing edge of the plate into a slot extending longitudinally along the surface of the plate cylinder. However, in order to properly attach the printing plate to the plate cylinder the leading and trailing edges are preferably formed with complimentary bends. Metallic plates are especially suited to receiving such bends due to their ability to plastically deform and retain a desired shape.
In order to form a printing plate properly so that the bend is uniform along the entire length of the printing plate, a plate bender is typically employed. One such well-known type of plate bender includes three adjacent rollers. The plate bender has a center mandrel roller that includes a longitudinal slot extending along its surface. The two remaining rollers act as guide rollers and are positioned on opposite sides of the mandrel and in rolling contact therewith. The mandrel is manually rotatable by way of a handle. The slot receives the leading edge of the printing plate, and when the user turns the mandrel the printing plate is forced between the mandrel and one of the surrounding guide rollers. Continued turning of the mandrel bends the plate and forms a crease at a point of the plate adjacent to the mandrel slot, thereby forming a permanent bend in the printing plate. After the plate is bent, the user would then turn the mandrel in the opposite direction so that the printing plate could be removed. The user then places the opposite end, or trailing edge, of the printing plate into the mandrel slot and rotates the mandrel in the opposite direction forming a crease and complimentary bend on the trailing edge.
Such a plate bender as described is extremely useful for bending the leading and trailing edges of a printing plate when the printing plate is made of a metallic material such as aluminum. However, in recent years it has become desirable to form printing plates out of nonmetallic materials, such as plastics. A plastic material found particularly suitable is polyester. One advantage of using the polyester sheets is that a user may create an image on a computer and then transfer the image directly to the polyester sheet. Reduced cost of the polyester plates is also a factor, especially for short printing runs. However, the polyester printing plates are not permanently bent as easily as the metallic sheets. Specifically, the leading and trailing edges of a polyester sheet when only mechanically deformed do not hold the required shape.
Prior art devices exist in order to form the edges of plastic sheets so that they can be secured to plate cylinders. One such device is marketed by Mitsubishi Paper Mills Ltd. These devices, called plate formers, are stand-alone units including a table surface on which a sheet is placed. Actuators are provided to apply mechanical pressure and heat to provide the proper edge configurations. However, these devices are relatively large, expensive machines that take up valuable floor space in a print shop. In addition, these machines are limited in their use since they can only be used with the polyester sheets and are not suitable for use with metallic or aluminum printing plates.
Accordingly, it would be desirable to provide a compact, easy to use plate bender that can effectively form the edges of a plastic printing plate. It would also be desirable to provide a plate bender which can be used to form both metallic and plastic printing plates.
It is an advantage of the present invention to provide a plate bender for forming a shaped edge on a printing plate that is made of a plastic material.
It is a further advantage of the present invention to provide plate bender having a heating element that forms the desired bend in a plastic printing plate.
It is a further advantage of the present invention to provide a plate bender for forming a shaped edge on a printing plate that is made of a either plastic or metallic material.
It is still a further advantage of the present invention to provide a plate bender that forms permanent bends on plastic printing plates and is easy to operate and is easily portable and requires no additional floor space.
It is yet a further advantage of the present invention to provide a plate bender with a rotatably mounted mandrel and a drive mechanism including a linkage, which moves the heater toward the substrate upon rotation of the mandrel.
In the efficient attainment of these and other advantages, the present invention provides a printing plate bender for forming shaped edges on a substrate including a frame and an elongate mandrel rotatably supported on the frame. The mandrel has a first substrate retainer supported thereon. A first elongate guide roller is rotatably supported on the frame and disposed adjacent to the mandrel. A heater is disposed in longitudinal alignment with the mandrel. The heater is movably mounted on the frame between a first position spaced from the mandrel and a second position wherein the heater is in close proximity to the substrate securable to the mandrel, thereby forming the shaped edge on the substrate. The heater is operatively connected to the mandrel such that rotation of the mandrel causes movement of the heater.
As more specifically described by way of the preferred embodiment, the substrate retainer may be a longitudinally extending slot formed in the mandrel adapted to receive an edge of the substrate. The longitudinal slot is preferably slightly wider than the thickness of the substrate, so that the substrate is closely held in the slot. In the preferred embodiment, the mandrel is operatively connected to the heater by a drive mechanism including an eccentric cam formed on one end of the mandrel and a carrier plate having a cam follower engagable with the cam. The carrier plate is positioned such that when the cam is rotated the heater moves between the first and second position. The cam is preferably connected to the rotational axis of the mandrel such that the amount of rotation of the mandrel is directly proportional to the amount of rotation of the cam. In the preferred embodiment the cam follower is the carrier member which is movably attached to the frame while at the same time being attached to the heater. The carrier member is preferably attached to the end plate of the frame, which is attached to the ends of the elongate mandrel. Preferably there is a handle connected to the mandrel which includes a shaft extending from the end thereof to permit the mandrel to be rotated. The mandrel may also include a second substrate retainer for accommodating a variety of printing plate materials. It is envisioned that either a plastic substrate such as polyester or metallic substrate such as aluminum may be used with the present invention.
Preferably, there is a controller operatively connected to the heater, which controls the amount of time that the heater is energized. The timer may be set to operate the heater for the specified amount of time depending on the substrate that is used. The timer preferably includes an indicator for advising the user when the bend in the substrate has been formed.